No, not all polyatomic ions have at least one dative covalent bond. Polyatomic ions can have a variety of bonding arrangements, including both ionic and covalent bonds.
A dative covalent bond, also known as a coordinate covalent bond, occurs when one atom donates a pair of electrons to another atom. This type of bond is typically represented by an arrow pointing from the donor atom to the acceptor atom.
While dative covalent bonds can be found in some polyatomic ions, it is not a requirement for all of them. Polyatomic ions can form through various bonding mechanisms, including the combination of ionic bonds and regular covalent bonds.
For example, the sulfate ion (SO4^2-) has covalent bonds within the sulfate molecule itself, but it also has ionic bonds with other ions when it forms ionic compounds. The covalent bonds in the sulfate molecule are formed by the sharing of electrons, while the ionic bonds are formed through the transfer of electrons from one atom to another.
Overall, the bonding in polyatomic ions can involve a combination of covalent and ionic bonds, depending on the nature and composition of the ion. Dative covalent bonds are just one possible type of bond that can occur in polyatomic ions, but they are not present in all cases.